An optical backbone network provides the functionality of communicating traffic of a client device through an optical fiber communication channel that connects nodes in accordance with a contract service quality (a service class). The optical backbone network receives a client signal through an interface between a node device and a client device. A plurality of client signals are multiplexed in a variety of multiplexing schemes, and then the signals are transmitted through a backbone transmission link with a larger capacity. Multiplexing schemes to be used include Wavelength Division Multiplexing (WDM), Time Division Multiplexing (TDM), Orthogonal Frequency Division Multiplexing (OFDM), or the like.
In optical backbone networks, ultrahigh capacity traffic with 100 Gbps (Giga bit per second) grade per channel is transmitted. Consequently, a fault recovery technique for failures due to an optical fiber disconnection or a breakdown of an optical node device, and a technique to improve the usage efficiency of optical frequency resources, become important in the optical backbone network.
The 1+1 protection system and the shared protection system are known as the fault recovery technique, and an example of those fault recovery techniques is described in Patent Literature 1.
A signal switching device described in Patent Literature 1 includes a signal switching unit, a branching unit to branch a user signal for redundancy, and a device monitoring control unit to monitor and control the entire device. The signal switching device transmits user signals to another signal switching device through an active route, a first backup route, and a second backup route. The other signal switching device receives the signals through the above-described routes, a signal monitoring unit monitors signal conditions in the active route and the backup routes, and a selecting unit selects and outputs a normal signal to a user device.
The signal switching unit is set to connect with the active route when the active route is normal. If failures occur in the active route, the selection unit in the switching device at the receiving side selects a signal transmitted through the first backup route and outputs it to the user device.
The signal monitoring unit in the backup path monitors the first backup route. When the signal monitoring unit detects a failure such as a signal disruption and an excess of threshold of error rate in the signal from the first backup route, the device monitoring control unit controls the signal switching unit to switch the connection from the first backup route to the second backup route.
It is said that the configuration described above can always keep a backup system working normally; consequently, a highly reliable 1+1 redundant configuration can be implemented that is capable of dealing with double failures in a device or a transmission link between transmitting and receiving nodes.
On the other hand, the elastic optical network system has been proposed in order to utilize efficiently optical frequency resources (see Patent Literature 2, for example). It is possible in the elastic optical network system to allocate the minimum necessary frequency band depending on the transmission capacity of the optical signal to a route between nodes through which the optical signal is transmitted and received on a network in which a plurality of nodes are connected through optical fibers. In addition, it is possible in the elastic optical network system to determine a frequency bandwidth to be allocated flexibly by the number of slots using a preset frequency width as a unit of a slot.
As mentioned above, according to the elastic optical network system, it is possible to change the required number of wavelength slots for an optical path depending on the required capacity of the traffic. This makes it possible to allocate optical paths to redundant wavelength resources that cannot be utilized in conventional networks with fixed grid, and improve the usage efficiency of the optical network.
Related techniques include techniques described in Patent Literature 3 to Patent Literature 5.